1. Field of the Invention
The present disclosure relates to a communication apparatus performing data communication such as facsimile communication.
2. Description of the Related Art
For instance, in a communication apparatus such as a facsimile apparatus, image data transmission and reception is performed. First, a transmission side transmits a request to start communication. Then, a reception side receives the request to start communication. Exchange of predetermined signals is performed and a communication path is established. After that, data transmission and reception is performed. Further, after receiving the request to start communication, when the data communication cannot be started because of being communicating with other communication apparatus or other reason, the reception side communication apparatus sends back a communication disabled notification to the transmission side communication apparatus. When receiving the communication disabled notification, the transmission side communication apparatus may wait to transmit the request to start communication again to the reception side communication apparatus (redial or retry). When the communication disabled notification is returned again after the retransmission, the transmission side communication apparatus will transmit the request to start communication repeatedly.
In order to avoid repetition of the redial (recall), there is known a facsimile apparatus, which is connected to an Integrated Services Digital Network, predicts a time period until a busy state is released when a calling is received during the busy state, and sets the predicted time period in a release completion message to be sent to a calling side facsimile apparatus.
Here, a communication line is used for retransmission of the request to start communication and reply of the communication disabled notification in response to the request to start communication. Repetition of the redial (resending of the request to start communication) is not preferred for efficient communication. In addition, when the data communication cannot be completed even if the redial is repeated the upper limit number of times, a communication error process is performed. When the communication error process is performed, the data remains to be unreached. Therefore, it is preferred to set the number of redial times to be as small as possible.
Here, in the known technique described above, the predicted time period is sent to the calling side facsimile apparatus. However, when there is an interrupt of an incoming call from other facsimile apparatus before calling based on the predicted time period, communication may start between the interrupting facsimile apparatus and the facsimile apparatus that has transmitted the predicted time period. Then, even if the redial is performed based on the predicted time period, data communication cannot be started because the communication is being performed. Then, the redial is required to be performed again. Therefore, the known technique also has the problem that repetition of the redial (recall) may occur.
In this way, the known technique is not sufficient to prevent the retransmission (redial) of the request to start communication, and has the problem that the redial is repeated so that communication efficiency may be largely decreased.